Wisdom teeth (third molars) are the last teeth to develop and appear in the mouth. The normal position of wisdom teeth is behind the upper and lower second molars. The jaws of modern humans are not normally large enough to accommodate the four wisdom teeth. This is why wisdom teeth are usually removed. When the wisdom tooth is blocked from erupting or coming into the mouth normally, it is termed "impacted". Serious problems may develop from impacted or partially impacted teeth such as pain, infection, formation of cysts, crowding of anterior teeth, and damage to adjacent teeth. If a cyst is formed and is not treated, a tumor may develop from the walls of the cyst and a more involved surgical procedure may be required for removal.